Printed wiring board, crack prediction device, and crack prediction method

ABSTRACT

A printed wiring board includes: a laminated body that has a plurality of wiring layers laminated therein; a first through hole that electrically connects two or more wiring layers with each other; and a second through hole that has strength to expansion and contraction of the laminated body less than in the first through hole.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2012-205868, filed on Sep. 19,2012, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a printed wiring board,a crack prediction device, and a crack prediction method.

BACKGROUND

In recent years, with downsizing and advancing functionality ofelectronics, printed wiring boards provided in electronics have highlydensified wiring. In addition, with advancing functionality ofelectronic components mounted on printed wiring boards, the temperatureof heat applied to such a printed wiring board is also rises. Forexample, a printed wiring board provided in electronics having strictdemands for security, such as electronics mounted in an automobile, alsohas a higher demanded upper temperature limit.

Printed wiring boards may include, for example, multilayered printedwiring boards that is possible to be downsized and highly densified (forexample, refer to Japanese Laid-open Patent Publication No. 04-208597).

A multilayered printed wiring board is equipped with a through holeelectrically connecting wiring patterns of each layer with each other.Japanese Laid-open Patent Publication Nos. 2007-318035 and 2009-164358are further examples of related art.

With the densification of wiring, through holes in printed wiring boardsare also being downsized. Compared with larger through holes, smallerthrough holes are poor in strength of an electrically conductivematerial in the through holes (for example, copper plating).

In addition, with advancing performance of electronic components,operation temperature of printed wiring boards is also becoming higher.Such a printed wiring board expands and contracts in accordance with achange in an ambient temperature.

For example, an epoxy resin used for a printed wiring board has agreater coefficient of thermal expansion compared with an electricallyconductive material formed in the through hole, so that thermal stressis applied to the electrically conductive material in the through holewhen the printed wiring board expands and contracts.

As just described, through holes are in a situation that is prone todevelop a crack associated with downsizing and a rise in temperature ofa printed wiring board. It is difficult not to expand and contract aprinted wiring board, which causes development of cracks, andintensification of structural strength of a through hole makes itdifficult to downsize a printed wiring board.

Consequently, it is considered that avoidance of defects in electronicsderived from a trouble in a printed wiring board is realistic action.

SUMMARY

According to an aspect of the invention, A printed wiring boardincludes: a laminated body that has a plurality of wiring layerslaminated therein; a first through hole that electrically connects twoor more wiring layers with each other; and a second through hole thathas strength to expansion and contraction of the laminated body lessthan in the first through hole.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is one example of a diagram illustrating a printed wiring board;

FIG. 2 is one example of a diagram of comparing dimensions of a throughhole for circuit with dimensions of a through hole for predictionaccording to a first example;

FIG. 3 is one example of a diagram of comparing dimensions of a throughhole for circuit with dimensions of a through hole for predictionaccording to a second example;

FIG. 4 is one example of a diagram of comparing a through hole forcircuit with a through hole for prediction according to a third example;

FIG. 5 is one example of a diagram illustrating a through hole forprediction according to a fourth example;

FIG. 6 is one example of a diagram illustrating a through hole forprediction according to a fifth example;

FIG. 7 is one example of a diagram of comparing lands around a throughhole for circuit with lands around a through hole for predictionaccording to a sixth example;

FIG. 8 is one example of a perspective view of a printed wiring boardhaving a through hole for circuit and a through hole for predictionaccording to a seventh example disposed therein;

FIG. 9 is one example of a structural diagram of a printed wiring boardhaving a through hole for circuit and a through hole for predictionaccording to an eighth example disposed therein;

FIG. 10 is one example of a state diagram of a through hole for circuitwhen a printed wiring board expands along a lamination direction of alaminated body;

FIG. 11 is one example of a state diagram of a through hole forprediction when a printed wiring board expands along a laminationdirection of a laminated body;

FIG. 12 is one example of a diagram illustrating a flowchart of amanufacturing procedure according to a first example;

FIGS. 13A through 13E are examples of drawings illustrating firstthrough fifth states of the manufacturing procedure according to thefirst example;

FIG. 14 is one example of a diagram illustrating a flowchart of amanufacturing procedure according to a second example;

FIGS. 15A through 15F are examples of drawings illustrating firstthrough sixth states of the manufacturing procedure according to thesecond example;

FIG. 16 is one example of a diagram illustrating an electronic componentthat is possible to predict a crack in a through hole equipped in aprinted wiring board;

FIG. 17 is one example of a diagram illustrating a lower side portion ofa CPU of a printed wiring board;

FIG. 18 is one example of a diagram illustrating an image of a circuitachieved by a detection circuit;

FIG. 19 is one example of a graph illustrating relationship between alapse time since use of an electronic component is started andresistance values of a through hole for prediction and a through holefor circuit; and

FIG. 20 is one example of a graph illustrating relationship between alapse time since use of an electronic component is started andresistance values of four through hole for prediction.

DESCRIPTION OF EMBODIMENTS

Descriptions are given below to embodiments. The embodiments describedbelow are merely illustrative and do not limit the present technicalscope to the following modes.

Embodiment of Printed Wiring Board

FIG. 1 is one example of a diagram illustrating a printed wiring board.A printed wiring board 1 is provided with a laminated body 2, a throughhole 3 for circuit (one example of “a first through hole”), and athrough hole 4 for prediction (one example of “a second through hole”).The laminated body 2 is a lamination of a plurality of wiring layers.The materials to constitute the laminated body 2 may be any, and a glasscloth cured with a resin, for example, suppresses expansion andcontraction in a lamination direction repeated due to a change intemperature and humidity compared with those using papers. As theexpansion and contraction of the laminated body 2 in a laminationdirection is suppressed, a possibility of fatigue failure of the throughholes formed in the laminated body 2 is reduced.

The through hole 3 for circuit electrically connects two or more wiringlayers with each other by joining copper plating 32, which is anelectrically conductive material formed on a wall of a through bore 31equipped in the laminated body 2 with lands 33 formed in each wiringlayer. In the through hole 4 for prediction, similar to the through hole3 for circuit, copper plating 42, which is a conductor formed on a wallof a through bore 41 equipped in the laminated body 2, is joined withlands 43 formed in each wiring layer. It is to be noted that the throughhole 4 for prediction is not intended to electrically connect eachwiring layer with each other, so that each land 43 is possible to beelectrically independent of the circuit formed in each wiring layer. Thethrough hole 4 for prediction is intended to predict a crack in thethrough hole 3 for circuit, and is designed to develop a crack prior tothe through hole 3 for circuit. That is, the printed wiring board 1according to the present embodiment is equipped with the through hole 4for prediction separate from the through hole 3 for circuit but in theidentical printed wiring board, thereby sensing a sign of cracks in thethrough hole 3 for circuit and enabling to take action before a crackcomes to be developed in the through hole 3 for circuit. The throughhole 3 for circuit and the through hole 4 for prediction are not limitedto those using copper plating and may also be those using anelectrically conductive material other than copper.

In the printed wiring board 1, a crack develops in the through hole 4for prediction prior to the through hole 3 for circuit. Therefore,monitoring the presence of a crack developed in the through hole 4 forprediction enables to predict a crack to be developed in the throughhole 3 for circuit. A crack to be developed in the through hole 3 forcircuit becomes predictable, thereby enabling to take variousprecautionary measures, such as, for example, component replacementintended to avoid a trouble and prior backup intended to avoid data lossassociated with a trouble. For example, in a case of electronics havinga possibility that a sudden trouble triggers an accident, such aselectronics for automobiles and medical equipment, it becomes possibleto carry out warning to avoid an unexpected trouble and the like.

The through hole 4 for prediction becomes possible to triggerdevelopment of cracks prior to the through hole 3 for circuit bydesigning as follows, for example.

FIRST EXAMPLE OF THROUGH HOLE FOR PREDICTION

FIG. 2 is one example of a diagram of comparing dimensions of thethrough hole 3 for circuit with dimensions of a through hole 4 forprediction according to a first example. The through hole 4 forprediction becomes possible to trigger development of cracks prior tothe through hole 3 for circuit by, for example, being designed in such amanner that strength to expansion and contraction in a laminationdirection of the laminated body 2 becomes lower than the strength of thethrough hole 3 for circuit compared with the through hole 3 for circuit.

For example, as the hole diameter of a through hole becomes smaller, thecross sectional area of copper plating of the through hole also becomessmaller with the square of the hole diameter. As the cross sectionalarea of the copper plating becomes smaller, the strength to the loadacting along the lamination direction of the laminated body decreases.With that, the through hole 4 for prediction according to the firstexample is designed to have, for example, as illustrated in FIG. 2, ahole diameter of the through hole 4 for prediction smaller compared withthe hole diameter of the through hole 3 for circuit. As the firstexample, compared with the through hole 3 for circuit, the through hole4 for prediction has a smaller hole diameter than the hole diameter ofthe through hole 3 for circuit, thereby making it possible to triggerdevelopment of cracks prior to the through hole 3 for circuit.

SECOND EXAMPLE OF THROUGH HOLE FOR PREDICTION

FIG. 3 is one example of a diagram of comparing dimensions of thethrough hole 3 for circuit with dimensions of a through hole 4 forprediction according to a second example. The through hole 4 forprediction becomes possible to trigger development of cracks prior tothe through hole 3 for circuit by, for example, being designed in such amanner that thermal stress applied from the lands 43 to copper plating42 becomes higher than the thermal stress to the through hole 3 forcircuit compared with the through hole 3 for circuit.

For example, since copper plating is joined with lands, when a force ina bending direction acts on the joint between the lands and the copperplating, a split and the like are prone to be developed in the copperplating. Particularly in the lands having a short length compared withlands having a long length, when the laminated body expands andcontracts in the lamination direction, a force in the bending directioncentered on the joint between the lands and the copper plating easilyacts. With that, the through hole 4 for prediction according to thesecond example is designed to have, for example, as illustrated in FIG.3, a length of lands 43 joined with the through hole 4 for predictionshorter than the length of lands 33 joined with the through hole 3 forcircuit. As the second example, the through hole 4 for prediction has ashorter length of lands 43 joined with the through hole 4 for predictionthan the length of lands 33 joined with the through hole 3 for circuit,thereby making it possible to trigger development of cracks prior to thethrough hole 3 for circuit.

THIRD EXAMPLE OF THROUGH HOLE FOR PREDICTION

FIG. 4 is one example of a diagram of comparing the through hole 3 forcircuit with a through hole 4 for prediction according to a thirdexample. The through hole 4 for prediction becomes possible to triggerdevelopment of cracks prior to the through hole 3 for circuit by, forexample, being designed in such a manner that a number of lands 43applying thermal stress to the copper plating 42 is more than the numberof lands that the through hole 3 for circuit has compared with thethrough hole 3 for circuit.

For example, magnitude of the load that is applied from the lands to thecopper plating varies depending on the number of joined lands. Withthat, the through hole 4 for prediction according to the third exampleis designed to have, for example, as illustrated in FIG. 4, a number oflands 43 joined with the through hole 4 for prediction more than thenumber of lands 33 joined with the through hole 3 for circuit. As thethird example, the through hole 4 for prediction has a more number oflands 43 joined with the through hole 4 for prediction than the numberof lands 33 joined with the through hole 3 for circuit, thereby makingit possible to trigger development of cracks prior to the through hole 3for circuit.

It is normally rare that the through hole 3 for circuit is electricallyconnected to circuits in all layers with wire and there is lesspossibility of joining the lands 33 all through the layers.Consequently, it is considered there are many cases that the number oflands 43 joining with the through hole 4 for prediction is possible tobe more than the number of lands 33 joining with the through hole 3 forcircuit.

FOURTH EXAMPLE OF THROUGH HOLE FOR PREDICTION

FIG. 5 is one example of a diagram illustrating a through hole 4 forprediction according to a fourth example. The through hole 4 forprediction becomes possible to trigger development of cracks prior tothe through hole 3 for circuit by, for example, being designed in such amanner that the members applying thermal stress to the copper plating 42is more than the members that the through hole 3 for circuit hascompared with the through hole 3 for circuit.

For example, thermal stress that is applied to the copper plating variesdepending on expansion and contraction of the member that makes contactwith the copper plating. With that, in the through hole 4 for predictionaccording to the fourth example, for example, as illustrated in FIG. 5,a material having a higher coefficient of thermal expansion than thecoefficient that the copper plating 42 has is injected into the throughhole. As the material having a higher coefficient of thermal expansionthan the coefficient that the copper plating 42 has is injected into thethrough hole, when the printed wiring board 1 repeats expansion andcontraction due to the heat cycle, the thermal stress of the materialinjected into the through hole is further applied to the copper plating42 of the through hole 4 for prediction. The material having a highercoefficient of thermal expansion than the coefficient that the copperplating 42 has may include, for example, a material similar to the resinthat forms the laminated body 2 and the like. As the fourth example, inthe through hole 4 for prediction, the material having a highercoefficient of thermal expansion than the coefficient that the copperplating 42 has is injected into the through hole, thereby making itpossible to trigger development of cracks prior to the through hole 3for circuit.

The material injected into the through hole 3 for circuit drags thecopper plating 32 associated with expansion of the material and takesthe role in further extending a crack developed in the copper plating42. Consequently, although possible to be applied alone, the fourthexample is more effective, for example, to be combined with any one ormore examples of the first through third examples in view of taking therole in secondarily triggering development of cracks.

FIFTH EXAMPLE OF THROUGH HOLE FOR PREDICTION

FIG. 6 is one example of a diagram illustrating a through hole 4 forprediction according to a fifth example. The through hole 4 forprediction becomes possible to trigger development of cracks prior tothe through hole 3 for circuit by, for example, equipping a pinhole 44in the copper plating 42 in advance. When the pinhole 44 is formed inthe copper plating 42 in advance, the pinhole 44 becomes a start ofcrack development. Therefore, when the printed wiring board 1 repeatsexpansion and contraction due to the heat cycle, the copper plating 42is prone to break around the pinhole 44. As the fifth example, in thethrough hole 4 for prediction, the pinhole 44 is formed, thereby makingit possible to trigger development of cracks prior to the through hole 3for circuit.

SIXTH EXAMPLE OF THROUGH HOLE FOR PREDICTION

FIG. 7 is one example of a diagram of comparing the lands 33 around thethrough hole 3 for circuit with lands 43 around a through hole 4 forprediction according to a sixth example. The through hole 4 forprediction becomes possible to trigger development of cracks prior tothe through hole 3 for circuit by, for example, being designed in such amanner that thermal stress applied from the laminated body 2 to copperplating 42 becomes higher than the thermal stress to the through hole 3for circuit compared with the through hole 3 for circuit.

For example, an amount of expansion and contraction in a laminationdirection of the laminated body 2 is proportional to the coefficient ofthermal expansion of the laminated body 2 in the lamination direction.For example, an electrically conductive material, such as copper,forming the lands has a smaller coefficient of thermal expansioncompared with the resin forming the laminated body 2. With that, forexample, as illustrated in FIG. 7, the lands 43 disposed around thethrough hole 4 for prediction is made less than the lands 33 disposedaround the through hole 3 for circuit. In such a manner, the coefficientof thermal expansion of the laminated body 2 around the through hole 4for prediction in a lamination direction becomes larger than thecoefficient of thermal expansion in a lamination direction around thethrough hole 3 for circuit. As a result, when the printed wiring board 1is thermally expanded, the laminated body 2 around the through hole 4for prediction expands larger than the laminated body 2 around thethrough hole 3 for circuit. The laminated body 2 around the through hole4 for prediction expands larger than the laminated body 2 around thethrough hole 3 for circuit, thereby making the through hole 4 forprediction possible to trigger development of cracks prior to thethrough hole 3 for circuit.

SEVENTH EXAMPLE OF THROUGH HOLE FOR PREDICTION

FIG. 8 is one example of a perspective view of the printed wiring board1 having the through holes 3 for circuit and the through holes 4 forprediction according to the seventh example disposed therein. Thethrough holes 4 for prediction are disposed in areas where, for example,the amount of expansion and contraction in a lamination direction of thelaminated body 2 is larger than areas where the through holes 3 forcircuit are disposed within the printed wiring board 1, thereby makingit possible to trigger development of cracks prior to the through hole 3for circuit.

For example, a great amount of thermal stress is prone to develop aroundan electronic component with relatively large heat generation, such as alarge scale integration (LSI) operating at high speed, like a centralprocessing unit (CPU) and a graphics processing unit (GPU), and anelectronic component with high power consumption. In particular, anelectronic component that is repeatedly turned on and off turns out tonot only generate heat at high temperatures but also to give thermalshock due to the change in temperature. With that, the through holes 4for prediction according to the seventh example are disposed, forexample, as illustrated in FIG. 8, at positions relatively close tosemiconductor devices 5 with great heat generation compared with thethrough holes 3 for circuit. The configuration of through holes 4 forprediction according to the seventh example may be same as the throughholes 3 for circuit or may also be same as any one of the first throughsixth examples. The through holes 4 for prediction are disposed atpositions closer to the semiconductor devices 5 than the through holes 3for circuit, thereby making it possible to trigger development of cracksprior to the through hole 3 for circuit.

EIGHTH EXAMPLE OF THROUGH HOLE FOR PREDICTION

FIG. 9 is one example of a structural diagram of the printed wiringboard 1 having the through holes 3 for circuit and a through hole 4 forprediction according to an eighth example disposed therein. The throughhole 4 for prediction is disposed, for example, as illustrated in FIG.9, near a central portion of the semiconductor device 5 in which a greatamount of thermal stress is particularly prone to develop within thesemiconductor device 5 of high heat generation. In the meanwhile, thethrough holes 3 for circuit are disposed, for example, as illustrated inFIG. 9, near the edge of the semiconductor device 5 with thermal stresssmaller than the thermal stress near the central portion within thesemiconductor device 5 of high heat generation. The through hole 4 forprediction according to the eighth example may have a configuration sameas the through holes 3 for circuit or may also have a configuration sameas any of the first through sixth examples. Even when being of anidentical electronic component, the through hole 4 for prediction isdisposed in a portion with thermal stress relatively smaller than thethrough holes 3 for circuit, thereby making it possible to triggerdevelopment of cracks prior to the through hole 3 for circuit.

The through hole 4 for prediction according to any one example of thefirst through eighth examples may also be combined, for example, with aconfiguration provided in a through hole 4 for prediction according toany other example.

The through hole 4 for prediction is not limited to any one example ofthe first through eighth examples or a combination of any one or moreexamples with each other. The through hole 4 for prediction may also bemade with, for example, the copper plating 42 having a thickness thinnerthan the copper plating 32 of the through hole 3 for circuit, therebymaking it possible to trigger development of cracks prior to the throughhole 3 for circuit.

In addition, the printed wiring board 1 is not limited to those having alarge number of wiring layers and may also be, for example, one havingtwo wiring layers or having three or more wiring layers.

ONE EXAMPLE OF DEVELOPMENT STATE OF CRACKS IN THROUGH HOLE FORPREDICTION

FIG. 10 is one example of a state diagram of the through hole 3 forcircuit when the printed wiring board 1 expands along a laminationdirection of the laminated body 2. The copper plating 32 has a smallercoefficient of thermal expansion compared with the coefficient ofthermal expansion of a material, such as a resin forming the laminatedbody 2. Consequently, when the temperature of the printed wiring board 1rises to expand the laminated body 2 along the lamination direction, thecopper plating 32 is pulled along the lamination direction.

FIG. 11 is one example of a state diagram of the through hole 4 forprediction when the printed wiring board 1 expands along the laminationdirection of the laminated body 2. The through hole 4 for prediction isdesigned in such a manner that a crack develops prior to the throughhole 3 for circuit. Therefore, when the printed wiring board 1 repeatsexpansion and contraction due to the heat cycle, a crack CR develops inthe copper plating 42 of the through hole 4 for prediction prior to thecopper plating 32 of the through hole 3 for circuit.

In FIGS. 10 and 11, state diagrams illustrating through holes that areequivalent to the through hole 3 for circuit and the through holes 4 forprediction according to the third example illustrated in FIG. 4.However, the state of the through hole when the laminated body 2 expandsalong the lamination direction is basically similar in any of the firstthrough eighth examples.

FIRST EXAMPLE OF METHOD OF MANUFACTURING PRINTED WIRING BOARD

It is possible to manufacture the printed wiring board 1 in, forexample, the following process. FIG. 12 is one example of a diagramillustrating a flowchart of a manufacturing procedure according to afirst example. Each diagram of FIGS. 13A through 13E is one exampleillustrating each state in the manufacturing procedure according to thefirst example. In the description of the following manufacturingprocess, although descriptions are given mainly to in a process offorming the through hole 4 for prediction, the through hole 3 forcircuit is also formed in the following manufacturing processsimultaneously.

In order to manufacture the printed wiring board 1, for example, awiring pattern 11 of an inner layer portion of the printed wiring board1 is formed in a substrate 12 (S101, FIG. 13A). Next, the substrates 12having the wiring pattern 11 formed therein are stacked on each otherfor lamination (S102, FIG. 13B). Next, a through bore 14 is formed in alaminated body 13 having the substrates 12 stacked therein (S103, FIG.13C). Next, a surface of the laminated body 2 is subjected to a resistand is immersed in a treatment liquid to form copper plating 15 on aninner wall of the through bore 14 (S104, FIG. 13D). Next, the wiringpattern 11 of an outer layer portion of the printed wiring board 1 isformed on a surface of the laminated body 13 (S105, in FIG. 13E).

The manufacturing process may also include a process other than theprocesses from step S101 to step S105. The manufacturing process of theabove one example is executed, thereby making it possible to fabricatethe printed wiring board 1 provided with the through hole 4 forprediction according to the first through eighth examples except thefifth example.

SECOND EXAMPLE OF METHOD OF MANUFACTURING PRINTED WIRING BOARD

In a case of forming the through hole 4 for prediction according to thefifth example illustrated in FIG. 6, it is possible to manufacture theprinted wiring board 1 in the following process, for example. FIG. 14 isone example of a diagram illustrating a flowchart of a manufacturingprocedure according to a second example. Each diagram of FIGS. 15Athrough 15F is one example illustrating a state of each manufacturingprocedure. In the description of the following manufacturing process,although descriptions are given mainly to in a process of forming thethrough hole 4 for prediction, the through hole 3 for circuit is alsoformed in the following manufacturing process simultaneously.

In order to manufacture the printed wiring board 1 equipped with thethrough hole 4 for prediction according to the fifth example, similar tothe above manufacturing method according to the first example, forexample, the wiring pattern 11 of an inner layer portion of the printedwiring board 1 is formed in a substrate 12 (S201, FIG. 15A). Next, aplating resist 16 is applied on a portion to form the through hole 4 forprediction (S202, FIG. 15B). The procedures after that are basicallysimilar to the manufacturing method according to the above firstexample. That is, the substrates 12 having the wiring pattern 11 formedtherein are stacked on each other for lamination (S203, FIG. 15C), andafter that, a through bore 14 is formed (S204, FIG. 15D). Next, copperplating 15 is formed on an inner wall of the through bore 14 (S205, FIG.15E). At this time, the portion of exposing the plating resist 16 withinthe inner wall of the through bore 14 is still in a state of not havingthe copper plating 32 formed therein, and the pinhole 44 is formed inthe copper plating 32. Next, the wiring pattern 11 of an outer layerportion of the printed wiring board 1 is formed on a surface of thelaminated body 13 (S206, in FIG. 15F). The manufacturing process mayalso include a process other than the processes from step S201 to stepS206.

Embodiment of Crack Prediction Device

FIG. 16 is one example of a diagram illustrating an electronic componentpossible to predict a crack in a through hole equipped in a printedwiring board. An electronic component 100 is an electronic componentapplicable to various electronics and has various components, such as anIC chip and a capacitor, mounted on the printed wiring board 1 describedabove. The electronic component 100 is provided with a detection circuit7 to monitor resistance of a through hole for prediction equipped in anarea where a CPU 6 to be at relatively high temperatures is disposedwithin the printed wiring board 1. The detection circuit 7 is linkedthrough the wiring pattern 11 to a connector 8 and the through hole forprediction. The electronic component 100 is provided with the throughhole for prediction and the detection circuit 7, so that it may beunderstood as a crack prediction device.

FIG. 17 is one example of a diagram illustrating a lower side portion ofthe CPU 6 of the printed wiring board 1. The electronic component 100according to the present embodiment is, for example, equipped with fourthrough holes 4A through 4D for prediction linked to the detectioncircuit 7 in the lower side portion of the CPU 6. The through holes 3for circuit are disposed appropriately in other areas.

FIG. 18 is one example of a diagram illustrating an image of a circuitachieved by the detection circuit 7. The through hole 4 for predictionis connected to a direct current power supply 101 to automaticallyadjust a voltage so as to flow a constant current and a voltagemonitoring circuit 102 to measure a voltage at both ends of the throughhole 4 for prediction. The voltage monitoring circuit 102 carries outmeasurement of a voltage, thereby monitoring a change in electricalresistance of the through hole 4 for prediction. Although FIG. 18illustrates one through hole 4 for prediction, similar circuits areachieved respectively for the other three through holes 4 forprediction.

FIG. 19 is one example of a graph illustrating relationship between alapse time since use of the electronic component 100 is started and theresistance values of the through hole 4 for prediction and the throughhole 3 for circuit. As the use of the electronic component 100 isstarted, the heat cycle is added to the through hole 4 for predictionand the through hole 3 for circuit and a resistance value graduallyincreases due to development of a minute crack and the like. Then, acrack develops in the through hole 4 for prediction prior to the throughhole 3 for circuit and the resistance value exceeds a predeterminedthreshold. As sensing that the resistance value of the through hole 3for circuit exceeds the predetermined threshold, the voltage monitoringcircuit 102 transmits a signal to outside of the electronic component100 through the connector 8. The threshold may be defined based on, forexample, a resistance change rate to an initial resistance value whenthe electronic component 100 is shipped and may also be defineduniformly for each product. The signal transmitted to outside of theelectronic component 100 is sent to, for example, a monitor, a speaker,and indicators linked to the electronic component 100 or sent to devicesexecuting a predetermined operation when the signal is sensed.

As long as a crack prediction device is achieved by the above electroniccomponent 100, it is enabled to take various precautionary measuresusing a signal outputted to outside. For example, in a case of beingapplied to an on-board electronics in car, displaying information on amonitor, a front panel, or the like of a car navigation device orplaying a message sound from a speaker or the like enables to tell amessage to encourage a user to repair or replacement of a component. Inaddition, in a case of a large scale information processing system, itis enabled to execute various processes in advance that have to beexecuted before the system comes to stop.

FIG. 20 is one example of a graph illustrating relationship between alapse time since use of the electronic component 100 is started andresistance values of the four through holes 4A through 4D forprediction. The through holes 4 for prediction may have defects in amanufacturing process and the like in some cases. For example, asillustrated in FIG. 20, it is assumed that one through hole forprediction (for example, in a case of FIG. 20, the through hole 4A forprediction) among the four through holes 4A through 4D for predictionhas a problem in manufacture, which causes a sudden crack to bedeveloped. In such a case, when a signal is immediately transmitted fromthe voltage monitoring circuit 102, it turns out to make the user totake useless action although the electronic component 100 is actuallypossible to be sufficiently used. With that, the voltage monitoringcircuit 102 may transmit a signal in a case that, for example, theelectrical resistances of any two, three, or four or more through holes4 for prediction among the four through holes 4A through 4D forprediction exceed a threshold. Crack development in the through hole 3for circuit is monitored in AND condition by the plurality of throughholes 4 for prediction, thereby enabling to avoid wrong advance noticeof crack development in the through hole 3 for circuit.

The electronic component 100 is not limited to those equipped with thefour through holes 4A through 4D for prediction, and for example, may bethose equipped with one through three through holes 4 for prediction andmay also be those equipped with five or more through holes 4 forprediction.

Each through hole 4 for prediction is not limited to those all beingplaced in the portion of the CPU 6 of high heat generation. Theelectronic component 100 may also have, for example, the through holes 4for prediction disposed in relatively low temperature areas other thanthe spots where the CPU 6 of high heat generation is placed within theprinted wiring board 1 to avoid wrong advance notice of crackdevelopment in the through hole 3 for circuit.

The crack prediction device is not limited to those carrying out advancenotice based on whether or not a resistance value of the through hole 4for prediction exceeds a predetermined threshold, and for example, mayalso carry out advance notice after the resistance of the through hole 4for prediction becomes fully open.

The crack prediction device is not limited to those achieved by theelectronic component 100 having various components mounted thereon. Thecrack prediction device may also have, for example, the detectioncircuit 7 mounted on a printed wiring board prepared separately from theelectronic component 100 equipped with the through hole for prediction.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A printed wiring board comprising: a laminatedbody that has a plurality of wiring layers laminated therein; a firstthrough hole that electrically connects two or more wiring layers witheach other; and a second through hole that has strength to expansion andcontraction of the laminated body less than in the first through hole.2. The printed wiring board according to claim 1, wherein the secondthrough hole has, compared with the first through hole, at least asmaller hole diameter, a shorter length of a land adjacent to the secondthrough hole, or a larger number of lands adjacent to the second throughhole.
 3. The printed wiring board according to claim 1, wherein thesecond through hole has a pinhole in an electrically conductive materialformed on an inner wall.
 4. The printed wiring board according to claim1, wherein the second through hole has a material having a coefficientof thermal expansion greater than an electrically conductive materialformed on an inner wall filled in the through hole.
 5. The printedwiring board according to claim 1, wherein the second through hole isdisposed in an area where a coefficient of thermal expansion is greaterthan an area where the first through hole is disposed within thelaminated body.
 6. The printed wiring board according to claim 1,wherein the second through hole is disposed in an area where atemperature becomes higher than an area where the first through hole isdisposed within the laminated body.
 7. The printed wiring boardaccording to claim 1, wherein the second through hole is electricallyconnected to a detection circuit to predict a crack in the first throughhole based on a change in electrical resistance.
 8. A crack predictiondevice comprising: a printed wiring board that has a laminated body witha plurality of wiring layers laminated therein, a first through holethat electrically connects two or more wiring layers with each other,and a second through hole that has strength to expansion and contractionof the laminated body less than in the first through hole; and adetection circuit that predicts a crack in the first through hole basedon a change in electrical resistance of the second through hole.
 9. Acrack prediction method comprising: monitoring a change in electricalresistance of a second through hole that has strength to expansion andcontraction of a laminated body less than in a first through holeequipped in a printed wiring board that has the laminated body with aplurality of wiring layers laminated therein and the first through holethat electrically connects two or more wiring layers with each other;and noticing a crack in the first through hole in advance when a changein electrical resistance of the second through hole is sensed.